This invention relates to a heating unit for use in a heater or drier, and, more particularly, to a device for heating fluid, in which is incorporated a heating unit having positive temperature coefficient (PTC) ceramic plates for heating fluid passing therethrough.
Such PTC ceramic plates can be employed as a heating means in which electrical energy is converted into thermal energy. When a suitable voltage is applied to a PTC ceramic material, such as s thermistor, the current flowing therethrough is comparatively high initially, so that the PTC ceramic material is heated rapidly up to a predetermined temperature. Thereafter, the current drops to a low value to reduce heat generation from the PTC ceramic, thus maintaining the predetermined temperature.
It is known to use the above described PTC ceramic material in the heaters for a heating unit in which fluid such as air or liquid to be heated passes closely by the PTC ceramic material,thus obtaining heat therefrom.
Referring to FIG. 7, showing a conventional type of heating unit, a plurality of PTC ceramic material heating elements b are aligned in parallel and spaced in relation to each other and are supported by four corner bars C1 to C4. Each PTC ceramic heating element b comprises a PTC ceramic heating body d having a pair of electrodes e1 and e2 provided at opposite end of PTC semiconductor heating body d. Since the corner bars are made of electrically conductive material, the corner bars C1 and C2 electrically connect respective electrodes e1, while the corner bars C3 and C4 electrically connect the other electrodes e2. When a suitable voltage is applied between the electrodes e1 and e2 through the corresponding corner bars, the electrical current flows through the PTC ceramic heating body d both in the inner region and at the outer region of the PTC semiconductor heating body d, thus energizing the PTC semiconductor heating body d to generate heat therefrom. It is apparent that the conventional type of heating unit as shown in FIG. 7 is not suitable for use in heaters or driers widely used nowadays.